Sunday, September 5, 2010

Abruptly Forgotten

Certain memories die suddenly rather than fading away

When you go from bed to bathroom on a dark night, a quick flick of the lights will leave a lingering impression on your mind’s eye. For decades evidence suggested that such visual working memories—which, even in daylight, connect the dots to create a complete scene as the eyes dart around rapidly—fade gradually over the span of several seconds. But a clever new study reported in the journal Psychological Science finds that such memories actually stay sharp until they are suddenly lost.

Cognitive psychologists Weiwei Zhang and Stephen J. Luck, both at the University of California, Davis, tested subjects’ recall for the hues of colored squares flashed briefly on a screen up to 10 seconds earlier. Subjects marked their answer on a color wheel. If memories decay gradually, the guesses should have become increasingly imprecise as time wore on, evidenced by participants selecting yellow or red, for example, when the correct choice was orange. Instead subjects went straight from fairly accurate answers to random choices—no better than chance—indicating the memories were decaying all at once. According to Zhang and Luck’s mathematical analysis, most subjects’ memories went “poof” somewhere between four and 10 seconds after the stimulus.

Researchers say a sudden die-off is to be expected if working memories are stored in circuits that feed back on themselves. Luck says the system is like a laptop as compared with a flashlight. “The laptop is an active system that uses feedback circuits to limit how much power it draws,” he says. So whereas a flashlight dims when it runs low on juice, “the computer runs perfectly normally while the battery drains,” he says, “until suddenly the laptop shuts off.”

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In its broadest sense, science (from the Latin scientia, meaning "knowledge") refers to any systematic knowledge or practice. In its more usual restricted sense, science refers to a system of acquiring knowledge based on scientific method, as well as to the organized body of knowledge gained through such research.

Fields of science are commonly classified along two major lines: natural sciences, which study natural phenomena (including biological life), and social sciences, which study human behavior and societies. These groupings are empirical sciences, which means the knowledge must be based on observable phenomena and capable of being experimented for its validity by other researchers working under the same conditions.